Modern vehicles have the front wheels suspended on a rigid front axle, the wheels each being mounted on a stub axle. The stub axles are articulated on the front axle by means of king pins which are supported at an upper and a lower bearing point on the stub axle. The front axle is fixed to the frame/chassis of the vehicle by means of two spring assemblies. For steering the vehicle, the stub axles are provided with steering arms that are connected to one another by a steering linkage and by a steering gear which transmits the steering angle from the steering wheel to the steering linkage and hence to the wheels.
Statutory requirements, particularly for heavy vehicles, govern various parameters of the steering mechanism. For example, the steering gear and the steering wheel must be designed so that a torque acting on the steering wheel will be capable of turning the wheels even when the power-assisted steering is defective.
Such a conventional steering system has a number of disadvantages. In a first instance, it is heavy. A complete steering system comprising (including, but not necessarily limited to) steering column, steering gear, one or two power steering units and the like may weigh several hundred kilograms. Secondly, a complicated wheel adjustment is required in order to align the angles of the steering system and the wheels relative to one another. Thirdly, a conventional power steering function is an unnecessary drain on energy. Fourthly, vehicles with different wheelbases and wheel installations require different Ackermann steer angles, which entails a number of different components for a whole range of vehicles. Fifthly the steering arms limit the maximum wheel angle which results in a limited turning circle radius. Sixthly vehicles with double front axles and/or multiple steered axles become extremely complicated.